It has long been a desire in the cooling system field to significantly extend the longevity of liquid coolants and/or cooling system components to approach or be coextensive with the lifetime of the motor vehicle or other power generating equipment with which the cooling system is used. In order to achieve this goal, it would be necessary to extend the corrosion inhibitor stability of liquid coolants to thereby limit the water content and resulting acidity within the coolants and their corrosive effects on engine surfaces and other cooling system components. An ideal such system would have to be low in water content at all times, and therefore would have to be capable of both significantly restricting the absorption of water into the coolant and forcing water out of the coolant.
U.S. Pat. No. 5,031,579, dated Jul. 16, 1991, shows a condenserless apparatus for cooling an internal combustion engine with a substantially anhydrous, boilable liquid coolant having a saturation temperature above that of water. The apparatus comprises a coolant chamber surrounding the cylinder walls and combustion chamber domes of the engine, and a coolant pump which is adapted to pump coolant through the coolant chamber at a flow rate so that the liquid coolant substantially condenses the coolant vaporized upon contact with the metal surfaces of the engine.
The apparatus of the '579 patent further comprises means for exhausting gases and/or vapors from the coolant chamber which is coupled in fluid communication with the coolant chamber at a location at or below ambient pressure. The means for exhausting preferably includes a conduit in fluid communication on one end with the coolant chamber, and an expansion tank in fluid communication with the other end of the conduit for receiving the gases and/or vapors from the coolant chamber and purging the gases through an outlet port into the ambient atmosphere. The liquid within the expansion tank is maintained at a level above the tank's connection to the conduit in order to provide a liquid barrier between the coolant chamber and the engine's ambient atmosphere.
The apparatus of the '579 patent further comprises a dehydrating unit coupled in fluid communication with an outlet port of the expansion tank for dehydrating the ambient air drawn into the expansion tank and thereby minimizing the exposure of the coolant to ambient vapors. Thus, an engine equipped with this type of apparatus can limit the amount of moisture returning to the coolant chamber by employing both the liquid barrier in the expansion tank and the dehydrating unit.
The apparatus of the '579 patent can use substantially non-aqueous coolants operating at ambient vent pressures, and therefore derives significant benefits over currently produced engine cooling systems. However, although the dehydrating unit provides significant advantages, it may be perceived in certain applications as being relatively bulky and thus undesirable. In addition, even when the engine is not running, the dehydrating unit will continue to absorb moisture, and thus requires periodic maintenance to remain effective. The preferred coolants in the apparatus of the '579 patent are forms of diols (e.g., propylene glycol) and are basically hygroscopic such that if exposed to ambient air, they will continue to absorb water vapor. If the dehydrating unit becomes saturated, it will permit moisture to pass into the expansion tank and in turn expose the coolant to undesirable levels of water. Thus, particularly at relatively low ambient temperatures (e.g., below about 10.degree. C. or 50.degree. F.), the liquid barrier in the expansion tank will not prevent the introduction of water vapor into the engine coolant chambers, but rather will absorb water.
The introduction of water into the coolant causes an increasing rate of degradation of the coolant, with the production of acids (oxsolic, acetic, etc.) and thus significantly limits the effective useful life of the coolant additives. This is discussed in further detail in my co-pending patent application Ser. No. 08/449,338, entitled "A Method Of Cooling A Heat Exchange System Using A Non-Aqueous Heat Transfer Fluid", which is hereby expressly incorporated by reference as part of the present disclosure.
Accordingly, it is an object of the present invention to overcome the drawbacks and disadvantages of the above-described cooling systems for internal combustion engines and other power generating equipment.